The bushing is a ring sleeve which acts as a gasket, in the Valve application field, and the bushing is inside the bonnet. General use of PTFE or graphite, such as corrosion-resistant materials, used for sealing effect, the role of the liner is to avoid shaft direct and seat hole on the grinding, reduce the damage to the shaft to protect the role of the shaft, so that the shaft in the liner to do reciprocating and rotation movement. such as valves, bearings and other components will use the bushing.